Abstract
Bidirectional phase-stabilized optical fiber links allow state-of-the-art optical clocks to be compared on a continental scale. However, intercontinental comparisons are still based on satellite techniques, preventing optical clocks from being compared without degradation. We performed the first optical frequency transfer experiment over submarine links, measuring levels of environmentally induced noise substantially lower than for on-land links. From these measurements, we predict the transfer stability that can be achieved over transoceanic links. We also performed the first optical frequency transfer over fibers installed in power cables, observing optical perturbations caused by the high-voltage field. Finally, we show that the low background noise of fibers on the seafloor allows applications in geophysical sensing.
Highlights
Fiber-based frequency transfer techniques have enabled the comparison of state-of-the-art optical atomic clocks over thousands of kilometers without degradation
Optical fiber links will play an instrumental role in the redefinition the second based on optical transitions [3] and the development of global timescales based on optical clocks
We reported on the first noise characterization of submarine fiber links for frequency metrology
Summary
Fiber-based frequency transfer techniques have enabled the comparison of state-of-the-art optical atomic clocks over thousands of kilometers (km) without degradation. Fiber-based optical frequency transfer experiments were performed only on telecommunication links installed on land. Optical fibers are sensitive to temperature variations [18], vibrations, and In both techniques, the highest compensation is achieved when the noise is the same in the forward and backward propagation. The highest compensation is achieved when the noise is the same in the forward and backward propagation This condition is met in fully bidirectional links, where the light is propagated in both directions through the same fiber. The noise we measured over the submarine links enables us to perform quantitative predictions on the level of transfer stability that can be achieved over transcontinental distances when two separate fibers are used for the two directions of propagation. We calculate that intercontinental comparisons of atomic clocks can be performed with the same or lower instability than satellite techniques, but in a ∼100 times shorter measurement time
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